High temperature field joints

ABSTRACT

A method for forming a high temperature field joint between two insulated pipe sections, and an insulated conduit having a low temperature field joint. The conduit comprises a steel pipe with a corrosion protection coating and a pipe insulation layer comprising a polymer composition having thermal conductivity of less than about 0.40 W/mk, and/or heat resistance to continuous operating temperatures from about 150° C. to above about 205° C. After a circumferential weld joint is formed between the two pipes, a first field joint insulation layer is applied over the joint area, the first field joint insulation layer comprises a polymer composition having heat resistance to continuous operating temperatures from about 150° C. to above about 205° C.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims priority to and the benefit of U.S. ProvisionalPatent Application No. 61/863,976 filed Aug. 9, 2013; and U.S.Provisional Patent Application No. 62/021,751 filed Jul. 8, 2014.

FIELD OF THE INVENTION

This invention relates to corrosion protection, mechanical protectionand insulation of welded joints between sections of coated pipe whichare to be incorporated into an undersea pipeline for carrying single ormulti-phase fluids such as oil, gas and water, particularly suchpipelines operating at temperatures from about 150° C. to above about205° C.

BACKGROUND OF THE INVENTION

Undersea pipelines may be formed from sections of steel pipe havingfactory-applied corrosion protection and insulating coatings. During themanufacture of insulated pipe, the ends of the pipe must be left bare toprevent damage to the coating when the pipes are joined in the field bywelding. Typically, the insulation layer is cut back from the end of thepipe to form a chamfer which is spaced from the end of the pipe. A lipof the corrosion protection layer may protrude beyond the end (or “toe”)of the chamfer. The chamfering step is typically performed in thefactory as part of the manufacturing process.

The individual pipe sections are joined together in the field to form acontinuous pipeline. The joints between the pipe sections are known as“field joints”, and are formed by butt welding the pipe sectionstogether, and then applying a layer of insulation over the bare pipesurrounding the weld joint. These steps may be performed as the pipelineis being reeled onto or from a lay vessel (so called “tie-in joints”),during pre-fabrication of multi-jointed pipe strings, or immediatelybefore laying of the pipeline. For reasons of economy, field joints mustbe rapidly formed and cooled to an acceptable temperature so as not toslow down the reeling or laying operation.

Processes for applying field joints to pipelines are disclosed incommonly assigned U.S. patent application Ser. No. 12/794,402 by Jacksonet al., which was published as US 2011/0297316 A1 on Dec. 8, 2011, andwhich is incorporated herein by reference in its entirety.

There is increasing demand in the oil and gas industry for higherperformance coatings to insulate and protect off-shore transportconduits operating at temperatures from about 150° C. to above 200° C.Examples of high temperature resistant pipeline coatings are disclosedin commonly assigned U.S. Provisional Patent Application No. 61/863,976by Wan et al., filed on Aug. 9, 2013, and in U.S. patent applicationSer. No. 14/193,663 by Edmondson et al., filed on Feb. 28, 2014, both ofwhich are incorporated herein by reference in their entireties.

Conventional field joint materials such as epoxy corrosion protectioncoatings and polyolefin insulation layers may not be suitable for use infield joints for pipelines operating at temperatures from about 150° C.to above 200° C. Therefore, there remains a need for reliable fieldjoint systems for use in high temperature fluid and/or gas transportconduits such as oil and gas pipelines, particularly those operating atthese high temperatures.

SUMMARY OF THE INVENTION

In an embodiment, there is provided a method for forming a field jointbetween two insulated pipe sections. The method comprises: (a) providinga first insulated pipe section and a second insulated pipe section,wherein each of the insulated pipe sections comprises: (i) a steel pipehaving an outer surface and an end, wherein an annular connectionsurface is located at said end of the steel pipe, (ii) a corrosionprotection coating provided over the outer surface of the steel pipe,wherein a terminal end of the corrosion protection coating is spacedfrom the end of the pipe; and (iii) a pipe insulation layer providedover the corrosion protection coating, wherein a terminal end of thepipe insulation layer is spaced from the end of the pipe, and whereinthe pipe insulation layer comprises a polymer composition having thermalconductivity of less than about 0.40 W/mk, and/or heat resistance tocontinuous operating temperatures from about 150° C. to above about 205°C. The corrosion protection coating and the pipe insulation layertogether comprise a line pipe coating of the insulated pipe sections;and each of the insulated pipe sections has a bare end portion in whichthe outer surface of the steel pipe is exposed, the bare end portionextending from the end of the steel pipe to the terminal end of eitherthe corrosion protection coating or the pipe insulation layer.

The method further comprises: (b) welding the steel pipe of the firstinsulated pipe section to the steel pipe of the second insulated pipesection, so as to form a circumferential weld joint between the annularconnection surfaces of the steel pipes, and so as to form a continuousjoint area which includes the circumferential weld joint and the bareend portions of the insulated pipe sections.

The method further comprises: (c) applying a first field jointinsulation layer over the joint area, wherein the first field jointinsulation layer comprises a polymer composition having heat resistanceto continuous operating temperatures from about 150° C. to above about205° C.

In another embodiment, there is provided an insulated conduit,comprising: (a) a first insulated pipe section and a second insulatedpipe section as defined above, with a circumferential weld joint betweenthe annular connection surfaces of the steel pipes, wherein a continuousjoint area includes the circumferential weld joint and the bare endportions of the insulated pipe sections.

The insulated conduit further comprises: (b) a field joint comprising:(i) a first field joint insulation layer over the joint area, whereinthe first field joint insulation layer comprises a polymer compositionhaving heat resistance to continuous operating temperatures from about150° C. to above about 205° C.

In yet another embodiment, the first field joint insulation layercomprises a silicone elastomer having heat resistance to continuousoperating temperatures from about 150° C. to above about 205° C., andwherein the silicone elastomer comprises a room temperature vulcanizing(RTV) silicone elastomer selected from the group comprising singlecomponent and dual component silicone elastomers.

In yet another embodiment, the first field joint insulation layer isapplied directly to the bare end portions of the insulated pipe sectionsin said joint area, and wherein the first field joint insulation layeris applied to a thickness which is substantially equal to a thickness ofthe line pipe coating.

In yet another embodiment, the method further comprises the step ofapplying a protective layer over the first field joint insulation layer,wherein the protective layer comprises an unfoamed polymeric materialand overlaps the line pipe coating on both sides of the first fieldjoint insulation layer.

In yet another embodiment, the method further comprises the step ofapplying an anti-corrosion coating to the joint area after the steelpipes are welded together, wherein the anti-corrosion coating comprisesa silicone elastomer having heat resistance to continuous operatingtemperatures from about 150° C. to above about 205° C., and wherein thefirst field joint insulation layer comprises a room temperaturevulcanizing (RTV) silicone elastomer selected from the group comprisingsingle component and dual component silicone elastomers.

In yet another embodiment, the silicone elastomer of the anti-corrosioncoating is a dual component RTV silicone elastomer; and the methodfurther comprises applying heat to the anti-corrosion coating to curethe silicone elastomer.

In yet another embodiment, a lip of the corrosion protection layerprotrudes beyond the terminal end of the pipe insulation layer of eachof the insulated pipe sections, and wherein the anti-corrosion coatingat least partially overlaps said lip.

In yet another embodiment, the method further comprises the step ofapplying a barrier layer over the terminal ends of the pipe insulationlayers, wherein the barrier layer comprises a RTV silicone elastomerwhich is applied to the terminal ends of the pipe insulation layerbefore the anti-corrosion coating is applied.

In yet another embodiment, the barrier layer is at least partially curedby application of heat before the anti-corrosion coating is applied tothe joint area.

In yet another embodiment, wherein the first field joint insulationlayer comprises a fluoroelastomer composition, such as a crosslinked,thermoset fluoroelastomer composition.

In yet another embodiment, the fluoroelastomer composition is applied tothe joint area in at least a partially uncured form, and thefluoroelastomer composition is cured by heating the pipe before and/orduring application of the first field joint insulation layer, or whereinthe fluoroelastomer composition is left in the uncured form.

In yet another embodiment, the first field joint insulation layercomprises hydrogenated nitrile butadiene rubber (HNBR), or a blend ofHNBR and a crosslinked, thermoset fluoroelastomer composition.

In yet another embodiment, the method further comprises the step ofapplying a second field joint insulation layer over the first fieldjoint insulation layer, wherein the second field joint insulation layercomprises a polymer composition having thermoplastic having heatresistance at continuous operating temperatures in a range from about90° C. to above about 140° C.

In yet another embodiment, the second field joint insulation layercomprises an epoxy-modified polymer network.

In yet another embodiment, the epoxy-modified polymer network comprisesa network epoxy modified urethane having heat resistance at continuousoperating temperatures in a range from about 90° C. to about 100° C.

In yet another embodiment, the first and second field joint insulationlayers have a combined thickness which is greater than that of the linepipe coating, and wherein the second field joint insulation layeroverlaps the line pipe coating on both sides of the joint area.

In yet another embodiment, the pipe insulation layer comprises a layerof a fluoroelastomer composition.

In yet another embodiment, the pipe insulation layer further comprises alayer of an elastomeric composition different from the fluoroelastomercomposition.

In yet another embodiment, a lip of the corrosion protection layerprotrudes beyond the terminal end of the pipe insulation layer of eachof the insulated pipe sections; wherein the first field joint insulationlayer is applied directly to the bare end portions of the insulated pipesections in said joint area; and wherein the first field jointinsulation layer at least partially overlaps said lip.

In yet another embodiment, the lip includes an outer layer comprisingthermal insulation of the same composition as an innermost layer of thepipe insulation layer.

In yet another embodiment, the first field joint insulation layer andthe outer layer of the lip are each comprised of a fluoroelastomer.

In yet another embodiment, the method further comprises the step ofapplying an adhesive layer or performing a surface activatingpretreatment to one or more layers of the field joint, so as to improveadhesion between said layers, wherein the surface activatingpretreatment is selected from flame treatment, corona dischargetreatment, and plasma treatment.

BRIEF DESCRIPTION OF THE DRAWINGS

The embodiments will now be described, by way of example only, withreference to the accompanying drawings in which:

FIG. 1 is a cross-sectional view of a pair of insulated pipe segmentsprior to being joined by welding;

FIG. 2 is a cross-sectional view showing the insulated pipe segments ofFIG. 1 after being joined by welding; and

FIGS. 3, 3A, 4 and 5 illustrate field joints according to specificembodiments of the invention.

DETAILED DESCRIPTION

A number of high temperature field joint systems and methods for forminghigh temperature field joints are now described below with reference tothe drawings.

The methods described herein are performed in the field during theconnection of insulated pipe sections to form a continuous pipeline. Asmentioned above, these steps are typically performed as the pipeline isreeled onto a lay vessel, during pre-fabrication of multi-jointed pipestrings, or as the pipeline is unreeled from a lay vessel.

FIG. 1 illustrates the end portions of a first insulated pipe section 10and a second insulated pipe section 12 to be joined and provided with afield joint. Each pipe section 10 or 12 may comprise a single length ofpipe, as supplied from a factory, or a partially assembled pipelinecomprising a plurality of pipe sections welded together end-to-end. Thepipe sections 10 and 12 are of a typical construction, as would beobtained from a pipe coating facility. As the end portions of the firstand second pipe sections 10, 12 shown in the drawings are of identicalconstruction, the same reference numerals will be used below and in thedrawings to identify their common elements.

Each pipe section 10, 12 includes a steel pipe 14 having a cylindricalouter surface 16. The end 15 of the pipe 14 has an annular connectionsurface 18 which is at a right angle to the outer surface 16. Theinsulated pipe sections 10, 12 have a line pipe coating comprising aplurality of layers. The line pipe coating includes at least a corrosionprotection layer 20 on the outer surface 16 of steel pipe 14, and a pipeinsulation layer 22 provided over the corrosion protection layer 20.

It will be appreciated that other functional layers may be integratedinto the line pipe coating of pipe sections 10, 12 without departingfrom the scope of the invention. For example, insulated pipe sections10, 12 may include more than one corrosion protection layer or more thanone layer of pipe insulation. In addition, pipe sections 10, 12 mayinclude other types of functional layers, such as thermal barriers,adhesive layers, and outer abrasion-resistant or protective top coats.The functional layers of the line pipe coatings of sections 10 and 12may include those described in above-mentioned U.S. Provisional PatentApplication No. 61/863,976 by Wan et al.

Although the corrosion protection layer 20 of the line pipe coating isdescribed herein as comprising a single layer, it may instead becomprised of multiple layers of different composition. The corrosionprotection layer 20 comprises a high temperature corrosion protectionmaterial and may be selected from the group comprising epoxy phenolics,polyphenylene sulphides, fluoropolymers, polyimides, or high temperaturefusion bonded epoxy (FBE), including modified versions and blendsthereof. For example, the FBE may be a high-temperature epoxy as definedin above-mentioned U.S. patent application Ser. No. 14/193,663 byEdmondson et al. Also, as disclosed by Edmondson et al., thehigh-temperature epoxy may comprise an epoxy novolac-based coatingcapable of continuous operation at or above about 200° C., wherein epoxynovolac resins comprise epoxy functional groups on a phenol formaldehydebackbone.

An adhesive layer may optionally be provided to bond the corrosionprotection layer 20 to the pipe surface 16 or to a subsequently appliedlayer.

The pipe insulation layer 22 comprises a polymer having a thermalconductivity of less than about 0.40 W/mk; for example about 0.10 to0.35 W/mK; and/or heat resistance at continuous operating temperaturesof at least about 200° C. For example, the pipe insulation layer 22 maycomprise a layer of fluoropolymer as described in above-mentioned U.S.Provisional Patent Application No. 61/863,976 by Wan et al. Thefluoropolymer may be a fluoroelastomer or a fluorocarbon thermoplasticas described by Wan et al. For example, pipe insulation layer 22 of FIG.1 includes a first, innermost layer 22A comprising a fluoropolymer.

In some embodiments, the pipe insulation layer 22 may comprise anelastomer selected from hydrogenated nitrile butadiene rubber (HNBR) andnitrile butadiene rubber (NBR). For example, a layer of NBR or HNBR canbe applied as a second layer 22B on top of an innermost layer 22A offluoropolymer. Alternatively, a layer of HNBR or a blend ofHNBR/fluoropolymer can be used as an innermost layer 22A of pipeinsulation in some systems. For example, where the innermost layer 22Acomprises HNBR, the maximum operating temperature of the system is about180° C. In the embodiment of FIG. 1, pipe insulation layer 22 includes asecond layer of insulation 22B located on top of the first layer 22A,wherein the second layer 22B comprises HNBR.

In some embodiments, the pipe insulation layer 22 may comprise a layerof thermoplastic or an epoxy-modified polymer network, as a furtherinsulating layer and/or as a protective topcoat. For example, thethermoplastic or epoxy-modified polymer network layer, such as a networkepoxy modified urethane or olefin, can be applied as a second layer 22Bon top of a first layer 22A which may comprise a fluoropolymer and/orHNBR, as discussed above. Alternatively, as shown in FIG. 1, thethermoplastic or epoxy-modified polymer network may be applied as athird layer 22C on top of the second layer 22B, and may comprise theoutermost layer of the line pipe coating. The compositions ofepoxy-modified polymer networks are further discussed below.

As shown in FIG. 1, each of the insulated pipe sections 10, 12 has abare end portion 24 in which the outer surface 16 of the steel pipe 14is exposed. The bare end portion 24 extends from the end 15 of pipe 14to a terminal end of either the corrosion protection layer 20 or thepipe insulation layer 22. The bare end portions 24 are formed duringmanufacturing and are provided to avoid damage to the layers 20, 22 whenthe ends of the insulated pipe sections 10, 12 are heated duringwelding. The lengths of the bare end portions 24 of pipe sections 10, 12may be the same or different, and depend at least partially on theequipment used for welding and/or field jointing, and on the steel pipewall thickness, and may be on the order of about 150-1,500 mm.

The pipe insulation layer 22 of each pipe section 10, 12 has a terminalend 26 which is spaced from the end 15 of pipe 14. The pipe insulationlayer 22 is provided with a chamfer 28 which commences at the terminalend 26 and slopes radially outwardly and away from the end 15 of pipe14, the chamfer 28 typically being sloped at an angle of from about 20to 60 degrees. The radially inward-most portion of the chamfer 28,located at the terminal end 26 of the pipe insulation layer 22, issometimes referred to herein as the “chamfer toe”.

The corrosion protection layer 20 of each insulated pipe section 10, 12may extend past the chamfer toe 26 such that a distance between theterminal end 30 of the corrosion protection layer 20 and the end 15 ofpipe 14 is less than a distance between the chamfer toe 26 and the end15 of pipe 14. Thus, the bare end portion 24 of each insulated pipesection 10, 12 extends from the end 15 of pipe 14 to the terminal end 30of the corrosion protection layer 20. This construction provides anexposed end portion 32 of the corrosion protection layer 20 whichextends beyond the chamfer toe 26, sometimes referred to herein as the“lip” of the corrosion protection layer 20. The axial length of lip 32is typically from about 5-50 mm, typically at least about 10 mm.

In some embodiments, as shown in the close-up of FIG. 3A, the lip 32 maycomprise multiple layers. The innermost layer 32A of a multi-layer lip32 comprises the exposed end portion of the corrosion protection layer20 described above. The multi-layer lip 32 also includes an outer layer32B of thermal insulation of the same composition as the insulationlayer 22, or the first layer 22A thereof, in the case of a multi-layerinsulation layer 22. The outer layer 32B of lip 32 will typically beintegrally formed with the insulation layer 22, for example by leaving alayer of thermal insulation when forming the chamfer 28. Typically, thelayers 32A and 32B may be of substantially the same thickness. Themulti-layer construction of lip 32 may be used, for example, where thefirst field joint insulation layer 6, described below, is of the same orsimilar composition as the insulation layer 22, or the first layer 22Athereof, so as to provide improved bonding between the first layer offield joint insulation 6 and the insulation layer 22 of the line pipecoating. In this embodiment, the anti-corrosion coating 38 of the fieldjoint coating may be eliminated, with the first layer of field jointinsulation 6 being applied directly to the outer surfaces 16 of pipes10, 12, optionally with the use of an adhesive layer (not shown) betweenthe pipe surface 16 and the first thermal insulation layer 6.

Prior to joining the pipes 10, 12 and applying the field jointinsulation system, the bare end portions 24 of the insulated pipesections 10, 12 may be subjected to a cleaning pretreatment in order toensure that the outer surfaces of the bare end portions 24 aresubstantially free from oil, grease, dirt, mill scale, rust, paint andforeign matter, so as to promote bonding with the field joint coating.The pretreatment may comprise a blast cleaning of the bare end portions24, which may be performed as an “off-line” step in the factory, forexample as disclosed in above-mentioned U.S. patent application Ser. No.12/794,402 by Jackson et al.

The insulated pipe sections 10, 12, are positioned end-to-end with theirannular connection surfaces 18 abutting one another, and are then buttwelded together to form a circumferential girth weld 34 as shown in FIG.2. During welding, the ends 15 of steel pipes 14 are heated to asufficiently high temperature for welding and a molten weld filler metalis applied to join the pipes 14 together and to fill any gaps betweenthe annular connection surfaces 18. After welding, and prior to furtherprocessing, the heated area is permitted to cool. The welding stepresults in the formation of a continuous circumferential weld joint 34between the annular connection surfaces 18 of steel pipes 14, and thisis shown in FIG. 2. The weld joint 34, together with the bare endportions 24 of insulated pipe sections 10, 12, form a continuous jointarea 36 which is defined herein as comprising the entire area over whichthe outer surfaces of pipes 14 are exposed. The steel pipes 14 of pipesections 10, 12 are locally heated proximate to their ends 15 during thewelding operation. The lengths of bare end portions 24 are of sufficientlengths to prevent excessive heating of the corrosion protection layer20 and the pipe insulation layer 22.

In some embodiments, an anti-corrosion coating 38 is applied to thejoint area 36 after welding. The anti-corrosion coating 38 has along-term resistance to temperatures from about 150° C. to above about205° C., and may comprise any of the materials mentioned above withreference to the corrosion protection layer 20, and optionally includingan adhesive layer.

Alternatively, the anti-corrosion coating 38 may comprise a siliconeelastomer having a long-term resistance to temperatures from about 150°C. to above about 205° C. The silicone elastomer may be a roomtemperature vulcanizing (RTV) silicone elastomer comprisingpolydimethylsiloxane. RTV silicone elastomers are curable at ambient andelevated temperatures, i.e. by condensation or addition curing. Forexample, suitable RTV elastomers for use in the anti-corrosion coatinginclude single component (RTV-1) silicone elastomers which are curableby condensation curing by reaction between hydroxyl groups of theelastomer and atmospheric moisture. Suitable RTV elastomers also includedual component (RTV-2) silicone elastomers which are curable bycondensation curing or by an addition reaction between vinyl functionalsiloxane polymers and silicon-hydrogen oligomers. Addition curing willproceed at ambient temperature but is significantly faster at elevatedtemperature. Also, the concentration of oligomer affects curing time,and therefore the curing time of the silicone elastomer can be tailoredby controlling the temperature and/or the concentration of oligomer.

The anti-corrosion coating 38 is applied over the entire joint area 36,including the weld joint 34 and the bare end portions 24, so as toprovide a continuous corrosion protection layer in the joint area 36.The anti-corrosion coating 38 may be applied by spraying or brushing toa thickness of about 100-2000 micrometers, for example about 500-1500micrometers.

The anti-corrosion coating 38 at least partially overlaps the exposedend portions 32 of corrosion protection layers 20. In order to improveadhesion to the anti-corrosion coating 38, the exposed lip 32 ofcorrosion protection layers 20 may be lightly abraded prior toapplication of the anti-corrosion coating 38, the abrasion beingperformed either in the factory or in the field.

Alternatively, or in addition to this abrasive pretreatment, an adhesivemay be applied to one or more of the chamfer 28, the chamfer toe 26, andthe exposed lip 32 of corrosion protection layer 20, so as to improveadhesion to the anti-corrosion coating 38 and/or to subsequently appliedinsulation layers. Alternatively, one or more of the chamfer 28, thechamfer toe 26, and the exposed lip 32 of corrosion protection layer 20may be surface activated by flame treatment, corona discharge treatment,or plasma treatment to create reactive functional groups on its outersurface to improve bonding to the anti-corrosion coating 38 and/or tosubsequently applied insulation layers.

The anti-corrosion coating 38 typically does not overlap the chamfers 28to any significant extent. In fact, the chamfer 28 may be masked, forexample with tape, so as to prevent the anti-corrosion coating 38 fromoverlapping the chamfer 28.

An alternate method of masking the chamfers 28 is to at least partiallycoat them with a chamfer inhibition barrier 50 so as to prevent directcontact between the chamfer 28 and any subsequently applied layers, asfurther discussed below with reference to FIGS. 3, 4 and 5. The chamferinhibition barrier 50 may comprise a layer of a RTV silicone elastomerwhich may be the same or different from the RTV silicone elastomercomprising the anti-corrosion coating 38. For example, the chamferinhibition barrier 50 may comprise an RTV-1 silicone elastomer,particularly in a system where the anti-corrosion coating 38 of thefield joint comprises a RTV-2 silicone elastomer, since the curing ofthe RTV-2 elastomer may be inhibited by the chemistry of certain typesof polymers used in the line pipe coating, such as fluoropolymers.

The chamfer inhibition barrier 50 may be applied by spraying or brushingto a thickness of about 100-2000 micrometers, for example about 500-1500micrometers. Because the chamfer inhibition barrier 50 is applied toprevent inhibition of curing in the anti-corrosion coating 38, it willonly need to be applied to the thickness of the anti-corrosion coating38. Therefore, the chamfer inhibition barrier 50 may only be requiredover the toe 26 of chamfer 28, as in FIG. 3.

An adhesive may be applied to the chamfer inhibition barrier 50 toimprove adhesion to the anti-corrosion coating 38. Such an adhesivelayer 52 is shown in FIG. 5 and discussed below with reference toEmbodiment 3. Alternatively, the chamfer inhibition barrier 50 may besurface activated by flame treatment, corona discharge treatment, orplasma treatment to create reactive functional groups on its outersurface to improve bonding to the anti-corrosion coating 38.

After it is applied to pipes 10, 12, the anti-corrosion coating 38 is atleast partly cured prior to further processing. Although anti-corrosioncoatings 38 comprising RTV silicone elastomers will eventually cure atambient temperatures, it may be desired to heat the anti-corrosioncoating 38 to accelerate curing. This may be accomplished by selectivelypre-heating the steel pipes 10, 12 within the joint area 36 immediatelybefore application of the anti-corrosion coating 38, or by heating theanti-corrosion coating 38 after it is applied.

The next step in the method is to apply a first field joint insulationlayer 6 over the joint area 36 and at least partially covering chamfers28. An adhesive may be applied to the anti-corrosion coating 38 and/orchamfers 28 to improve adhesion to subsequently applied insulationlayers. Alternatively, the anti-corrosion coating 38 and/or the chamfers28 may be surface activated by flame treatment, corona dischargetreatment, or plasma treatment to create reactive functional groups onits outer surface to improve bonding to the subsequently appliedinsulation layers.

Due to its proximity to the outer surfaces 16 of pipes 10, 12, the firstfield joint insulation layer 6 has a long-term resistance totemperatures from about 150° C. to above about 205° C. The first fieldjoint insulation layer 6 is also designed to exhibit adequatecompressive creep resistance and modulus at these temperatures, andhence maintain the required thermal insulation properties over thelifetime of the oil and gas recovery project. In addition, thecompositions should be sufficiently ductile to withstand the bendingstrains experienced by the insulated pipe during reeling andinstallation operations.

In some embodiments, the first field joint insulation layer 6 comprisesa high temperature resistant fluoroelastomer and/or HNBR selected toprovide the first field joint insulation layer 6 with one or more of thefollowing properties:

thermal conductivity of less than about 0.40 W/mk; for example about0.10 to 0.35 W/mK, typically from about 0.15-0.30 W/mK;

heat resistance at continuous operating temperatures within the rangefrom about 150° C. to above about 205° C.

The first field joint insulation layer 6 may be foamed or solid. Wherethe first field joint insulation layer 6 is foamed, it may either be ablown foam or a syntactic foam having a degree of foaming of up to about50%, for example from about 5% to about 30%.

The first field joint insulation layer 6 is applied at a sufficientthickness to provide the insulated transport conduit with an acceptableheat transfer coefficient (U) for the conditions under which it is to beused, with U typically being in the range from about 1 to about 10W/m²K, for example from about 2 to about 8 W/m²K.

The thickness of the first field joint insulation layer 6 is highlyvariable, due to the fact that each pipeline system is designed for useunder specific conditions of depth, temperature etc., and also dependingon whether or not the field joint includes one or more additional layersof thermal insulation. In some embodiments, the thickness of the firstfield joint insulation layer 6 ranges from about 10 mm to a thicknesswhich is greater than that of the line pipe coating.

For example, the first field joint insulation layer 6 may comprise afluoropolymer composition, which provides the first field jointinsulation layer 6 with heat resistance at the above-mentioned operatingtemperatures, resistance to chemicals and harsh environments, strength,processibility etc. The fluoropolymer may comprise a crosslinked(vulcanized) fluoroelastomer or a fluorocarbon thermoplastic. Thefluoropolymer composition of the first field joint insulation layer 6may either be solid or a syntactic foam, and may comprise any of thecompositions disclosed in above-mentioned U.S. Provisional PatentApplication No. 61/863,976 by Wan et al.

For example, suitable fluoropolymer compositions may, for example,comprise copolymers of tetrafluoroethylene (TFE) and propylene, alsoknown as TFE/P or FEPM copolymers, which are fluoroelastomerspredominantly comprised of tetrafluoroethylene units (—CF₂—CF₂—) andpropylene units (—CH₂—CH(CH₃)—).

Alternate fluoroelastomers which may be used in the first field jointinsulation layer include those known as Type 1 to Type 5 FKMs,including:

Type 1 FKMs comprising copolymers of vinylidene fluoride (VDF) andhexafluoropropylene (HFP), such as those known as Viton™, Dyneon™,Dai-EI™, Tecnoflon™ and Fluorel™;

Type 2 FKMs comprising terpolymers of VDF, HFP and tetrafluoroethylene(TFE);

Type 3 FKMs comprising copolymers of VDF, HFP, TFE andperfluoromethylevinyl ether (PMVE);

Type 4 FKMs comprising terpolymers of VDF, TFE and propylene; and

Type 5 FKMs comprising copolymers of VDF, HFP, TFE, PMVE, ethylene FFKMperfluoroelastomers (such as Kalrez™, Tecnoflon PFR™, and Perlast™), andfluorosilicone rubbers (FVMQ).

Instead of an elastomer, the fluoropolymer may comprise a fluorocarbonthermoplastic such as perfluoroalkoxy (PFA) copolymer ofpolytetrafluoroethylene and perfluoro alkyl vinyl ether;polytetrafluoroethylene (PTFE); fluorinated ethylene propylene (FEP); acopolymer of tetrafluoroethylene and hexafluoroethylene; and/orpolyvinylidene fluoride (PVDF).

A suitable fluoroelastomer composition for use in the first field jointinsulation layer 6 is commercially available from AGC Chemicals (AsahiGlass Co., Ltd.) under the trademark AFLAS™. For example, suitablefluoroelastomer compositions include AFLAS™ 100, AFLAS™ 150, and AFLAS™300, based on copolymers having the repeating structure—(CF₂CF₂)—(CH₂CH(CH₃))_(m)—; and AFLAS™ 200, based on copolymers havingthe repeating structure —(CF₂CF₂)—(CH₂CH(CH₃))_(m)—(CF₂CF₂)_(n)—. AFLAS™copolymer compositions provide the first field joint insulation layer 6with high heat resistance and high chemical resistance.

Once crosslinked, the fluoropolymer composition is a thermoset material,and does not soften or melt when heated. For example, the decompositiontemperature of the crosslinked propylene-tetrafluoroethylene copolymeris about 415° C.

It will be appreciated that the fluoropolymer compositions comprisingthe first field joint insulation layer 6, as discussed above, may alsobe used in the pipe insulation layer 22 of the line pipe coating.

In other embodiments, the first field joint insulation layer 6 maycomprise a silicone elastomer having long-term resistance totemperatures from about 150° C. to above about 205° C., including any ofthe RTV-1 and RTV-2 silicone elastomers mentioned above.

As mentioned above, the first field joint insulation layer 6 maycomprise HNBR having long-term resistance to temperatures from about150° C. to about 180° C. Alternatively, the first field joint insulationlayer 6 may comprise a blend of HNBR with one of the fluoropolymersmentioned above, such blends having long-term resistance to temperaturesgreater than the maximum for HNBR (about 180° C.) and less than themaximum for fluoropolymers (above about 205° C.).

As for the method of application, the first field joint insulation layer6 may be applied to the joint area 36 by casting, wherein an annularmold is applied over the joint area 36 and the mold cavity is filledwith the first field joint insulation layer 6 in the form of a moltenresin. The mold may optionally be left in place over the joint toprovide the field joint with an outer shell. In an alternativemethodology, the field joint insulation may also be applied via wrappingof extruded or pre-prepared sheets or strips, or the application ofpre-formed shells, wherein the sheets, strips of shells are eitheruncured or partially cured when applied to the joint area 36.

In some of the embodiments disclosed herein, the first field jointinsulation layer 6 is applied over the anti-corrosion coating 38. Asmentioned above, the anti-corrosion coating 38 may be provided with anadhesive layer or may be subjected to a surface-activating pre-treatmentto improve adhesion with the first field joint insulation layer 6.

In other embodiments, the anti-corrosion coating 38 is eliminated andthe first field joint insulation layer 6 is applied directly to the barepipes 10, 12 in the weld joint area 36, optionally with an adhesivebetween the pipes 10, 12 and the insulation layer 6. These embodimentsmay be used in situations where both the line pipe insulation layer 22and the field joint insulation layer 38 comprise a fluoropolymer, andwhere the lip 32 includes an outer layer 32B comprised of the line pipethermal insulation.

The first field joint insulation layer 6 may be cured immediately uponapplication to the joint area 36. In some embodiments, the curing of thefirst field joint insulation layer 6 may be assisted by the applicationof heat to the joint area 36. In this regard, the joint area 36 may bepre-heated by induction heating of the steel pipes 10, 12, for exampleby advancing the pipe sections 10, 12 through an induction heatingapparatus which selectively preheats the steel pipe in the joint area 36immediately before application of the first field joint insulation layer6.

In some embodiments, the first field joint insulation layer 6 may becured in operation. In these embodiments, the first field jointinsulation layer 6 is left partially or completely uncured after it isapplied, and is subsequently cured when the insulated pipeline is heatedduring use.

In embodiments where the first field joint insulation layer 6 is theonly layer of thermal insulation applied to the joint area 36, the firstfield joint insulation layer 6 is applied to a thickness sufficient tocompletely fill the volume of the joint area 36, completely covering thechamfers 28 of the pipes 10, 12, and possibly overlapping the linecoatings of the pipes 10, 12 on both sides of the joint area 36.

In other embodiments, the first field joint insulation layer 6 may beapplied as a thermal barrier, so as to only partially fill the volume ofthe joint area 36. In these embodiments, the field joint will include atleast a second field joint insulation layer 8 applied over the firstfield joint insulation layer 6. Depending on the compositions of thefirst and second insulation layers 6, 8, it may be desired to include alayer of adhesive between layers 6 and 8 so as to improve interlayeradhesion. Alternatively, the first field joint insulation layer 6 may besurface activated by flame treatment, corona discharge treatment, orplasma treatment to create reactive functional groups on its outersurface to improve bonding to the subsequently applied second layer 8.

Because the outer surface of the first field joint insulation layer 6will be at a lower temperature than the operating temperature of theconduit, when the conduit is in use, the second field joint insulationlayer 8 may not necessarily require the same level of high temperatureresistance. Therefore, the composition of the second field jointinsulation layer 8 is highly variable.

For example, the second field joint insulation layer 8 may comprise athermoplastic, such as conventional polyethylene, polypropylene,polybutylene, polyurethane and copolymers, blends and elastomersthereof. Alternatively, the second field joint insulation layer 8 maycomprise any of the thermoplastics disclosed in US Patent ApplicationPublication No. US 2009/0159146 A1 by Jackson et al. or U.S. Pat. No.8,397,765 by Jackson et al., both of which are incorporated herein byreference in their entireties. The second field joint insulation layer 8may instead comprise an elastomeric material different from that of thefirst field joint insulation layer 6, such as a hydrogenated nitrilebutadiene rubber (HNBR), nitrile butadiene rubber (NBR), siliconerubber, ethylene propylene diene monomer (EPDM) rubber, or butyl rubber.

In a specific embodiment, the second field joint insulation layercomprises an epoxy-modified polymer network, such as an epoxy-urethanehybrid system or an epoxy-olefin hybrid system. Such systems aresometimes referred to as network epoxy modified urethanes or networkepoxy modified olefins. These epoxy-modified polymer networks typicallyhave a temperature rating from about 90° C. to about 140° C.

The second field joint insulation layer 8 may be foamed or solid. Wherethe second field joint insulation layer 8 is foamed, it may either be ablown foam or a syntactic foam having a degree of foaming of up to about50%, for example from about 5% to about 30%.

The thickness of the second field joint insulation layer 8 is alsohighly variable and, in some embodiments, the second field jointinsulation layer 8 may extend to a thickness greater than that of theline pipe coating.

As mentioned above, one or more of the field joint insulation layers mayalso be provided with an additional protective layer, or topcoat 9comprised of unfoamed polymeric material. The topcoat 9 may be preparedfrom the same or different material as one of the underlying field jointinsulation layers 6 and/or 8, or a modified or reinforced versionthereof. Alternatively, the topcoat 9 may comprise a metal shell.

It may be required, for example, to impart a higher degree of physicalor chemical performance, such as impact, abrasion, crush or moistureresistance, to the outer surface of the insulated pipe, in which case itmay be advantageous to prepare the outer protective topcoat 9 from apolymeric material having superior impact, abrasion, crush or chemicalresistance to that from which the field joint insulation layer, orlayers, is made. Such a material may comprise the thermal insulationmaterial blended with suitable polymeric modifiers, compatibilisers, orreinforcing fillers or fibres, or it may comprise a dissimilar,preferably compatible, polymeric material.

Any of the thermal insulation layers may contain additives selected fromone or more members of the group comprising inorganic fillers,reinforcing fillers or fibres, nano-fillers, conductive fillers,flame-retardant fillers, antioxidants, heat-stabilisers, process aids,compatibilisers, organic fillers, and pigments.

Specific embodiments of the above-described field joint systems andmethods are described below, with reference to FIGS. 3 to 5. It will beappreciated that the thicknesses of the layers and coatings shown inFIGS. 3 to 5 are not shown to scale.

The insulated pipe segments 10, 12 according to the followingembodiments are provided with a line pipe coating comprising:

1. a corrosion protection layer 20 applied directly to the bare outersurface 16 of the pipes 10, 12, the layer 20 comprising an epoxyphenolic;

2. an adhesive layer (not shown) applied over the corrosion protectionlayer 20;

3. a first pipe insulation layer 22A comprising a fluoroelastomercomposition, applied over the adhesive layer;

4. a second pipe insulation layer 22B comprising an elastomeric materialdifferent from that of the first pipe insulation layer 22A, such as aHNBR and/or NBR;

5. a third pipe insulation layer 22C comprising an epoxy-modifiedpolymer network as described above, for example network epoxy modifiedurethane.

The line pipe coating has a chamfer 28 with an exposed lip 32 of thecorrosion protection layer 20 extending at least 10 mm past the chamfertoe 26.

Embodiment 1 (FIG. 3)

The chamfers 28 of pipes 10, 12 were optionally masked by applying achamfer inhibition barrier 50 comprising a silicone elastomer, such asany of the RTV-1 silicone elastomers described above, to at least thetoes 26 of chamfers 28. The chamfers 28 were preheated to about 100° C.before the chamfer inhibition barrier 50 was applied to chamfers 28 byspraying. The thickness of the chamfer inhibition barrier 50 was about1000 micrometers. The chamfer inhibition barrier 50 was cured by heating(baking).

Optionally, an anti-corrosion coating 38 comprising a siliconeelastomer, such as any of the RTV-2 silicone elastomers described above,was then applied to the joint area 36, to at least partially overlapsthe lip 32 of the corrosion protection layer 20. The anti-corrosioncoating has a thickness of about 500 to 1,500 micrometers and is appliedby spraying. The anti-corrosion coating 38 was cured by heating(baking).

A first field joint insulation layer 6 in the form of a thermal barrierwas then applied over the joint area 36, partially filling the jointarea 36 and partially overlapping the chamfers 28. The layer 6 compriseda fluoroelastomer composition (AFLAS™), which was applied in uncured orpartially cured form in the form of a sheet which is wrapped around thejoint area 36. The fluoroelastomer had a temperature rating of about205° C. and a thickness of about 50 mm.

Before, during and/or after the application of the first field jointinsulation layer 6, the steel pipes 10, 12 were induction heated to atleast partially cure the first field joint insulation layer 6. However,as discussed above, this curing step is optional, and the first fieldjoint insulation layer 6 may instead be cured during operation of thepipeline. The joint area 36 and chamfers 28 were then pre-heated toabout 80° C. and a second field joint insulation layer 8 was appliedover the first field joint insulation layer 6. The second field jointinsulation layer 8 was applied by casting in a sheet metal mold to asufficient thickness to completely fill the joint area 36, completelycover the remainder of chamfers 28, and overlap the outer surface of theline pipe coating. The total thickness of the second field jointinsulation layer was about 50-60 mm, and the overlap at each end of thejoint area 36 was about 8 mm in thickness and about 70 mm in axiallength.

Depending on the compositions of the first and second insulation layers6, 8, it may be desired to include a layer of adhesive between layers 6and 8 so as to improve interlayer adhesion. Alternatively, the firstfield joint insulation layer 6 may be surface activated by flametreatment, corona discharge treatment, or plasma treatment to createreactive functional groups on its outer surface to improve bonding tothe subsequently applied second layer 8. The surface activation mayoptionally be used in combination with the heating step discussed above.The second field joint insulation layer 8 comprised a network epoxymodified urethane composition having a temperature rating of about 95°C. The network epoxy modified urethane composition cures exothermicallyand no external heat was required to cure the second field jointinsulation layer 8. Instead of the network epoxy modified urethanecomposition, the second field joint insulation layer 8 may havecomprised a network epoxy modified olefin composition.

Embodiment 2 (FIG. 4)

The chamfers 28 of pipes 10, 12 were masked by applying a chamferinhibition barrier 50 comprising a silicone elastomer, such as any ofthe RTV-1 silicone elastomers described above. The chamfers 28 werepreheated to about 100° C. prior to application of the chamferinhibition barrier 50 by spraying to a thickness of about 1000micrometers. The chamfer inhibition barrier 50 was fully cured byheating (baking).

An adhesive layer 52 was then applied over the chamfers 28. The adhesivelayer comprised a RTV-1 silicone elastomer was applied to chamfers 28 byspraying to a thickness of about 1000 micrometers. The chamferinhibition barrier was semi-cured by heating (baking).

A first field joint insulation layer 6 was then applied over theadhesive layer 52 and over the entire joint area 36. The first fieldjoint insulation layer 6 comprised a silicone elastomer, such as any ofthe RTV-2 silicone elastomers described above, and was applied bycasting in a sheet metal mold to a sufficient thickness to completelyfill the joint area 36 and completely cover the chamfers 28, so as to besubstantially flush with the outer surface of the line pipe coating. Thetotal thickness of the first field joint insulation layer 6 was about80-100 mm.

A polyethylene heat shrink sleeve was then applied over the firstinsulation layer 6 as a protective shield or top coat 9. The sleeveoverlapped each end of the joint area 36 by an axial length of about 70mm.

Embodiment 3 (FIG. 5)

The chamfers 28 of pipes 10, 12 were partially masked by applying achamfer inhibition barrier 50 comprising a silicone elastomer, such asany of the RTV-1 silicone elastomers described above. The chamfers 28were preheated to about 100° C. prior to application of the chamferinhibition barrier 50 by spraying to a thickness of about 1000micrometers. The chamfer inhibition barrier 50 was fully cured byheating (baking).

An adhesive layer 52 was then applied over the masked portions ofchamfers 28. The adhesive layer 52 comprised a RTV-1 silicone elastomerand was applied to chamfers 28 by spraying to a thickness of about 1000micrometers. The adhesive layer 52 was semi-cured by heating (baking).

A first field joint insulation layer 6 was then applied over theadhesive layer. The first field joint insulation layer 6 comprised asilicone elastomer, such as any of the RTV-2 silicone elastomersdescribed above, and was applied by casting in a sheet metal mold topartially fill the joint area 36 and partially overlap the chamfers 28to a thickness of about 50-60 mm.

A second field joint insulation layer 8 was then applied over the firstinsulation layer 6. Prior to applying the second layer 8, the firstlayer 6 was preheated to about 80° C. to remove surface moisture and tohelp cure the subsequently applied second layer 8. Also, the first fieldjoint insulation layer 6 was surface activated so as to ionize thesilicone to create reactive functional groups on the surface of thefirst layer 6 and improve adhesion to the subsequently applied secondlayer 8. The surface activation comprised flame treatment, coronadischarge treatment, or plasma treatment.

The second field joint insulation layer 8 comprised a network epoxymodified urethane composition having a temperature rating of about 95°C. The second field joint insulation layer 8 was applied by casting in asheet metal mold to a sufficient thickness to completely fill the jointarea 36, completely cover the remainder of chamfers 28, and overlap theouter surface of the line pipe coating. As mentioned above, the secondfield joint insulation layer 8 may have comprised a network epoxymodified olefin composition, and/or the sheet metal mold may have beenleft in place to provide an outer metal shell over the field joint. Thetotal thickness of the second field joint insulation layer 8 was about50 mm, and the overlap at each end of the joint area 36 was about 8 mmin thickness and about 70 mm in axial length.

Where adhesive layers are mentioned herein, it will be appreciated thatthe composition of the adhesive layer will depend at least partly on thecompositions of the layers being bonded together. For example, adhesivesused herein may be polymers or reactive systems with functionalitieshaving mutual affinity to the layers being bonded, the functionalitiesbeing specific to the chemical composition of the layers being bonded.Preferably the adhesive should provide a bond strength sufficient topromote cohesive failure between the layers being bonded.

The adhesive layer between adjacent thermal insulation layers andbetween a thermal insulation layer and one or more of adjacent layersmay, for example, comprise a grafted polymer or copolymer, or polymerblend with one or more moieties compatible with each of the individuallayers to be bonded.

In embodiments where the first thermal insulation layer 6 comprises afluoroelastomer, the first thermal insulation layer 6 may be bonded toan adjacent layer by an adhesive which bonds to the fluoroelastomerduring vulcanization. Such an adhesive may be a liquid adhesivespecially formulated for vulcanization/bonding of elastomers to steeland other rigid substrates, such as those disclosed in above-mentionedU.S. Provisional Patent Application No. 61/863,976 by Wan et al.

Although the invention has been described in connection with corrosionprotection, mechanical protection and insulation of welded jointsbetween sections of coated pipe sections, it will be appreciated thatthe layered field joint coatings described herein may also be applied toother components of subsea oil and gas production systems, includingcomponents having more complicated, non-linear structures. Suchcomponents include bends, flanges, manifolds, valves, fittings, etc.,and other components of subsea oil and gas production systems requiringcorrosion protection, mechanical protection and/or thermal insulation.Therefore, as used herein, terms such as “pipe”, “pipe section”,“pipeline” and “insulated conduit” include other components of subseaoil and gas production systems, including those named above.

Although the invention has been described in connection with certainembodiments, it is not limited thereto. Rather, the invention includesall embodiments which may fall within the scope of the following claims.

What is claimed is:
 1. A method for forming a field joint between twoinsulated pipe sections, the method comprising: (a) providing a firstinsulated pipe section and a second insulated pipe section, wherein eachof the insulated pipe sections comprises: (i) a steel pipe having anouter surface and an end, wherein an annular connection surface islocated at said end of the steel pipe, (ii) a corrosion protectioncoating provided over the outer surface of the steel pipe, wherein aterminal end of the corrosion protection coating is spaced from the endof the pipe; and (iii) a pipe insulation layer provided over thecorrosion protection coating, wherein a terminal end of the pipeinsulation layer is spaced from the end of the pipe, and wherein thepipe insulation layer comprises a polymer composition having thermalconductivity of less than about 0.40 W/mk, and/or heat resistance tocontinuous operating temperatures from about 150° C. to above about 205°C.; wherein the corrosion protection coating and the pipe insulationlayer together comprise a line pipe coating of the insulated pipesections; and wherein each of the insulated pipe sections has a bare endportion in which the outer surface of the steel pipe is exposed, thebare end portion extending from the end of the steel pipe to theterminal end of either the corrosion protection coating or the pipeinsulation layer; (b) welding the steel pipe of the first insulated pipesection to the steel pipe of the second insulated pipe section, so as toform a circumferential weld joint between the annular connectionsurfaces of the steel pipes, and so as to form a continuous joint areawhich includes the circumferential weld joint and the bare end portionsof the insulated pipe sections; (c) applying a first field jointinsulation layer over the joint area, wherein the first field jointinsulation layer comprises a polymer composition having heat resistanceto continuous operating temperatures from about 150° C. to above about205° C.
 2. The method of claim 1, wherein the first field jointinsulation layer comprises a silicone elastomer having heat resistanceto continuous operating temperatures from about 150° C. to above about205° C., and wherein the silicone elastomer comprises a room temperaturevulcanizing (RTV) silicone elastomer selected from the group comprisingsingle component and dual component silicone elastomers.
 3. The methodof claim 2, wherein the first field joint insulation layer is applieddirectly to the bare end portions of the insulated pipe sections in saidjoint area, and wherein the first field joint insulation layer isapplied to a thickness which is substantially equal to a thickness ofthe line pipe coating.
 4. The method of claim 3, further comprising thestep of applying a protective layer over the first field jointinsulation layer, wherein the protective layer comprises an unfoamedpolymeric material and overlaps the line pipe coating on both sides ofthe first field joint insulation layer.
 5. The method of claim 1,further comprising the step of applying an anti-corrosion coating to thejoint area after the steel pipes are welded together, wherein theanti-corrosion coating comprises a silicone elastomer having heatresistance to continuous operating temperatures from about 150° C. toabove about 205° C., and wherein the first field joint insulation layercomprises a room temperature vulcanizing (RTV) silicone elastomerselected from the group comprising single component and dual componentsilicone elastomers.
 6. The method of claim 5, wherein the siliconeelastomer of the anti-corrosion coating is a dual component RTV siliconeelastomer; wherein the method further comprises applying heat to theanti-corrosion coating to cure the silicone elastomer.
 7. The method ofclaim 5, wherein a lip of the corrosion protection layer protrudesbeyond the terminal end of the pipe insulation layer of each of theinsulated pipe sections, and wherein the anti-corrosion coating at leastpartially overlaps said lip.
 8. The method of claim 7, furthercomprising the step of applying a barrier layer over the terminal endsof the pipe insulation layers, wherein the barrier layer comprises a RTVsilicone elastomer which is applied to the terminal ends of the pipeinsulation layer before the anti-corrosion coating is applied.
 9. Themethod of claim 8, wherein the barrier layer is at least partially curedby application of heat before the anti-corrosion coating is applied tothe joint area.
 10. The method of claim 5, wherein the first field jointinsulation layer comprises a crosslinked, thermoset fluoroelastomercomposition.
 11. The method of claim 10, wherein the fluoroelastomercomposition is applied to the joint area in at least a partially uncuredform, and wherein the fluoroelastomer composition is cured by heatingthe pipe before and/or during application of the first field jointinsulation layer, or wherein the fluoroelastomer composition is left inthe uncured form.
 12. The method of claim 5, wherein the first fieldjoint insulation layer comprises hydrogenated nitrile butadiene rubber(HNBR), or a blend of HNBR and a crosslinked, thermoset fluoroelastomercomposition.
 13. The method of claim 1, further comprising the step ofapplying a second field joint insulation layer over the first fieldjoint insulation layer, wherein the second field joint insulation layercomprises a polymer composition having thermoplastic having heatresistance at continuous operating temperatures in a range from about90° C. to above about 140° C.
 14. The method of claim 13, wherein thesecond field joint insulation layer comprises an epoxy-modified polymernetwork.
 15. The method of claim 14, wherein the epoxy-modified polymernetwork comprises a network epoxy modified urethane having heatresistance at continuous operating temperatures in a range from about90° C. to about 100° C.
 16. The method of claim 13, wherein the firstand second field joint insulation layers have a combined thickness whichis greater than that of the line pipe coating, and wherein the secondfield joint insulation layer overlaps the line pipe coating on bothsides of the joint area.
 17. The method of claim 1, wherein the pipeinsulation layer comprises a layer of a fluoroelastomer composition. 18.The method of claim 17, wherein the pipe insulation layer furthercomprises a layer of an elastomeric composition different from thefluoroelastomer composition.
 19. The method of claim 1, wherein a lip ofthe corrosion protection layer protrudes beyond the terminal end of thepipe insulation layer of each of the insulated pipe sections; whereinthe first field joint insulation layer is applied directly to the bareend portions of the insulated pipe sections in said joint area; andwherein the first field joint insulation layer at least partiallyoverlaps said lip.
 20. The method of claim 19, wherein the lip includesan outer layer comprising thermal insulation of the same composition asan innermost layer of the pipe insulation layer.
 21. The method of claim19, wherein the first field joint insulation layer and the outer layerof the lip are each comprised of a fluoroelastomer.
 22. The method ofclaim 1, further comprising the step of applying an adhesive layer orperforming a surface activating pretreatment to one or more layers ofthe field joint, so as to improve adhesion between said layers, whereinthe surface activating pretreatment is selected from flame treatment,corona discharge treatment, and plasma treatment.
 23. An insulatedconduit, comprising: (a) a first insulated pipe section and a secondinsulated pipe section, wherein each of the insulated pipe sectionscomprises: (i) a steel pipe having an outer surface and an end, whereinan annular connection surface is located at said end of the steel pipe,(ii) a corrosion protection coating provided over the outer surface ofthe steel pipe, wherein a terminal end of the corrosion protectioncoating is spaced from the end of the pipe; (iii) a pipe insulationlayer provided over the corrosion protection coating, wherein a terminalend of the pipe insulation layer is spaced from the end of the pipe, andwherein the pipe insulation layer comprises a polymer composition havingthermal conductivity of less than about 0.40 W/mk, and/or heatresistance to continuous operating temperatures from about 150° C. toabove about 205° C., wherein the corrosion protection coating and thepipe insulation layer together comprise a line pipe coating of theinsulated pipe sections; and (iv) a circumferential weld joint betweenthe annular connection surfaces of the steel pipes, wherein a continuousjoint area includes the circumferential weld joint and the bare endportions of the insulated pipe sections; (b) a field joint comprising:(i) a first field joint insulation layer over the joint area, whereinthe first field joint insulation layer comprises a polymer compositionhaving heat resistance to continuous operating temperatures from about150° C. to above about 205° C.
 24. The insulated conduit of claim 23,wherein the first field joint insulation layer comprises a siliconeelastomer having heat resistance to continuous operating temperaturesfrom about 150° C. to above about 205° C., and wherein the siliconeelastomer comprises a room temperature vulcanizing (RTV) siliconeelastomer selected from the group comprising single component and dualcomponent silicone elastomers.
 25. The insulated conduit of claim 24,wherein the first field joint insulation layer is applied directly tothe bare end portions of the insulated pipe sections in said joint area,and wherein the first field joint insulation layer is applied to athickness which is substantially equal to a thickness of the line pipecoating.
 26. The insulated conduit of claim 25, further comprising aprotective layer over the first field joint insulation layer, whereinthe protective layer comprises an unfoamed polymeric material andoverlaps the line pipe coating on both sides of the first field jointinsulation layer.
 27. The insulated conduit of claim 23, furthercomprising an anti-corrosion coating over the joint area, wherein theanti-corrosion coating comprises a silicone elastomer having heatresistance to continuous operating temperatures from about 150° C. toabove about 205° C., and wherein the first field joint insulation layercomprises a room temperature vulcanizing (RTV) silicone elastomerselected from the group comprising single component and dual componentsilicone elastomers.
 28. The insulated conduit of claim 27, wherein thesilicone elastomer of the anti-corrosion coating is a cured, dualcomponent RTV silicone elastomer.
 29. The method of claim 27, wherein alip of the corrosion protection layer protrudes beyond the terminal endof the pipe insulation layer of each of the insulated pipe sections, andwherein the anti-corrosion coating at least partially overlaps said lip.30. The insulated conduit of claim 29, further comprising a barrierlayer provided between the terminal ends of the pipe insulation layersand the anti-corrosion coating, wherein the barrier layer comprises aRTV silicone elastomer, wherein the barrier layer is at least partiallycured.
 31. The insulated conduit of claim 27, wherein the first fieldjoint insulation layer comprises a fluoroelastomer composition.
 32. Theinsulated conduit of claim 27, wherein the first field joint insulationlayer comprises hydrogenated nitrile butadiene rubber (HNBR), or a blendof HNBR and a crosslinked, thermoset fluoroelastomer composition. 33.The insulated conduit of claim 23, further comprising a second fieldjoint insulation layer over the first field joint insulation layer,wherein the second field joint insulation layer comprises a polymercomposition having thermoplastic having heat resistance at continuousoperating temperatures in a range from about 90° C. to above about 140°C.
 34. The insulated conduit of claim 33, wherein the second field jointinsulation layer comprises an epoxy-modified polymer network.
 35. Theinsulated conduit of claim 34, wherein the epoxy-modified polymernetwork comprises a network epoxy modified urethane having heatresistance at continuous operating temperatures in a range from about90° C. to about 100° C.
 36. The insulated conduit of claim 33, whereinthe first and second field joint insulation layers have a combinedthickness which is greater than that of the line pipe coating, andwherein the second field joint insulation layer overlaps the line pipecoating on both sides of the joint area.
 37. The insulated conduit ofclaim 23, wherein the pipe insulation layer comprises a layer of afluoroelastomer composition.
 38. The insulated conduit of claim 37,wherein the pipe insulation layer further comprises a layer of anelastomeric composition different from the fluoroelastomer composition.39. The insulated conduit of claim 23, wherein a lip of the corrosionprotection layer protrudes beyond the terminal end of the pipeinsulation layer of each of the insulated pipe sections; wherein thefirst field joint insulation layer is provided directly on the bare endportions of the insulated pipe sections in said joint area; and whereinthe first field joint insulation layer at least partially overlaps saidlip.
 40. The insulated conduit of claim 39, wherein the lip includes anouter layer comprising thermal insulation of the same composition as aninnermost layer of the pipe insulation layer.
 41. The insulated conduitof claim 40, wherein the first field joint insulation layer and theouter layer of the lip are each comprised of a fluoroelastomer.
 42. Theinsulated conduit of claim 23, further comprising one or more adhesivelayers, each of which is applied between adjacent layers of the fieldjoint, so as to improve adhesion between said layers.
 43. The insulatedconduit of claim 23, one or more layers of the field joint having beensubjected to a surface activating pretreatment selected from flametreatment, corona discharge treatment, and plasma treatment.